Systems and Methods of Wavelength Division Multiplex Passive Optical Networking

ABSTRACT

Example embodiments of a time division duplex (TDD) Wavelength Division Multiplex Passive Optical Network (WDM PON) architecture using passive optical splitters are disclosed herein. The disclosed TDD WDM PON includes fixed wavelength optical transmitters in an Optical Line Termination system with tunable receiver colorless Optical Network Units (ONUs) that reuse the downstream CW light to carry upstream data. The same wavelength may be used for downstream and upstream transmissions on a single fiber in the ODN. In this architecture, the number of ONUs may be greater than the number of transmitters at the OLT, allowing for a highly scalable system with capacity for growth. An example embodiment of the disclosed system uses Arrayed Waveguide Grating (AWG) or WDM filters at the OLT and a passive optical splitter in the field.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/509,146, filed on Oct. 8, 2014, which isincorporated by reference herein.

TECHNICAL FIELD

The present disclosure is generally related to telecommunications and,more particularly, is related to optical network systems.

BACKGROUND

Current systems of time division multiplexing passive optical network(TDM PON), such as non-limiting examples of GPON, XGPON1, EPON, and 10GEPON, can be categorized as sharing wavelength architectures. In TDM,each transmitter transmits during a slice of the transmission period. Anoptical network unit (ONU) is a device that transforms incoming opticalsignals into electronics at a customer's premises in order to providetelecommunications services over an optical fiber network. In TDM PON,multiple ONUs share the wavelength, or the bandwidth of a particularwavelength in TDM fashion.

In order to provide higher bandwidth per ONU, next generation PONsexplore the bandwidth of a fiber, i.e. utilize the full spectrum of afiber rather than an individual wavelength. One method to increase thebandwidth per ONU is to assign a dedicated wavelength to each ONU. Manywavelength division multiplexing (WDM) PON architectures are based onwavelength routers. Either thin film filter or arrayed waveguide grating(AWG) technologies may be used in WDM PON architectures. An arrayedwaveguide grating permits a single optical fiber to carry multiplechannels or communication bands. Fiber optic cables use very thin glassfibers to transmit light signals containing voice or datacommunications.

Light passes through air or fiber cables as a series of waves, similarlyto waves in water. The principle of light diffraction, where lightpassing through fibers of slightly different lengths exits at slightlydifferent phases or angles, is the basis for an arrayed waveguidegrating. Light exits each of the fibers in the waveguide at a slightlydifferent point in the wave because each fiber has a different length,and the light takes more or less time to travel its length. When theseout-of-phase frequencies interact, they create a diffraction pattern,which is a series of evenly spaced light signals, each with its ownfrequency.

In WDM, different frequencies of the light signal are used for differentcommunication bands, and the arrayed waveguide grating is used tocombine or multiplex these individual bands into a single fiber cable,allowing for many conversations or data streams to be combined. Theprocess can be reversed at the other end of a transmission line, withthe combined signals separated in a de-multiplexing waveguide.

There are few parts to an arrayed waveguide grating. The incoming fibercable is connected to a mixing zone, with multiple fiber cables. Thearrayed waveguide is lined up in a row at the other end of the zone. Atthe opposing end is a collection or focusing zone where the differentwavelengths or channels are separated by diffraction and enter multiplefiber cables.

FIG. 1 provides system diagram 100 of a WDM PON architecture using anarray of multiple wavelength transmitters as light sources in an opticalline termination (OLT) system. An AWG is used in the field to routewavelengths to the ONUs using the cyclic property of an AWG to routeupstream light from ONUs back to the OLT. The array of either fixed orgeneral wavelength transmit lasers send the different wavelengths ontransmission line 140 and all the wavelengths are coupled to one fiber.Multi-wavelength transmitter array 110 is coupled to fiber 140 atcoupler 130, transmitting each wavelength, λ₁ to λ_(N), on the fiber.The downstream transmission signals are received at AWG 150 and thensplit out to individual ONUs with transmit/receive pairs 160, 170 atcustomer premises. In this implementation, the upstream data streams aresent at a wavelength of λ_(N+1), which is the receive wavelength+Nwavelength steps. The signals are combined in AWG 150 to fiber 140 andreceived at the head end by receiver array 120. ONU 160 uses a cyclicproperty of AWG 150 to send λ_(N+1), to the same port and the samefilter on the same fiber. At the head end, there's a separate filter atthe receiver. At the receiver array, there's another filter so theλ_(N+1) gets separated to the appropriate receiver. So in this case, oneODN and one fiber handle both the upstream and the downstreamtransmissions.

Wavelength router based WDM PONs have many advantages. For instance, thepassive AWG has much lower loss than an active power splitter and itsloss is independent of the number of wavelengths. Additionally, WDM PONhas the potential of supporting more ONUs than does GPON or EPON, etc.However, there are large numbers of GPON and EPON systems alreadydeployed in the field that use passive optical power splitters. Thereare heretofore unaddressed needs to reuse power splitters for WDM PONwith these previous solutions.

SUMMARY

Example embodiments of the present disclosure provide systems ofwavelength division multiplex passive optical networking. Brieflydescribed, in architecture, one example embodiment of the system, amongothers, can be implemented as follows: an optical line termination (OLT)transmitter laser of a plurality of OLT transmitter lasers configured totransmit at a particular wavelength; and a wavelength router configuredto couple a downstream optical signal from the OLT transmitter laseronto a single fiber optical distribution network for reception by apassive optical power splitter, the wavelength router further configuredto receive an upstream optical signal from the single fiber opticaldistribution network and route the upstream optical signal to anappropriate receiver.

Embodiments of the present disclosure can also be viewed as providingmethods for wavelength division multiplex passive optical networking. Inthis regard, one embodiment of such a method, among others, can bebroadly summarized by the following steps: receiving an optical signal;modulating the optical signal with an optical line terminationtransmitter laser at a particular wavelength; and transmitting themodulated signal to a wavelength router for transmission on a singlefiber optical distribution network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram of an example embodiment of a WDM PONarchitecture using multiple wavelength transmitters array as lightsources.

FIG. 2 is a system block diagram of an example embodiment of systems andmethods of WDM PON with a wavelength router at the central office andpassive optical power splitter at the optical distribution network.

FIG. 3 is a system block diagram of an example embodiment of the OLT ofthe WDM PON of FIG. 2 with an out of band control channel.

FIG. 4 is a system block diagram of an example embodiment of the OLT ofthe WDM PON of FIG. 2 with a single in-band C band and/or L band controlchannel.

FIG. 5 is a system block diagram of an example embodiment of the ONU ofthe WDM PON of FIG. 2 with an out of band control channel.

FIG. 6 is a system block diagram of an example embodiment of the ONU ofthe WDM PON of FIG. 2 with a single in-band C band and/or L band controlchannel.

FIG. 7 is a system block diagram of an example embodiment of the OLT andONU of the WDM PON of FIG. 2 with an out of band control channel.

FIG. 8 is a system block diagram of an example embodiment of the OLT andONU of the WDM PON of FIG. 2 with an in-band C band and/or L bandcontrol channel.

FIG. 9 is a system block diagram of an example embodiment of the ONU ofFIG. 6 with an SOA.

FIG. 10 is a system block diagram of an example embodiment of the ONU ofFIG. 5 with an SOA.

FIG. 11 is a flow diagram of an example embodiment of a method ofwavelength division multiplexing passive optical networking.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described more fullyhereinafter with reference to the accompanying drawings in which likenumerals represent like elements throughout the several figures, and inwhich example embodiments are shown. Embodiments of the claims may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. The examples set forthherein are non-limiting examples and are merely examples among otherpossible examples.

In order to meet a seamless migration, an improved system should bebackward compatible with current passive optical power splitter ODNsystems. This brings several challenges to the WDM PON architecturedesigns. WDM PONs may use the existing GPON/EPON fiber plant with nowavelength router used in the field. Additionally, there should not be asecond fiber for upstream transmission. Issues to be overcome includeassigning upstream wavelengths to each ONUs; routing upstreamwavelengths back to OLTs since there is no wavelength router in thefield; and solving wavelength contingency problem if upstreamtransmissions use the same wavelength as downstream transmissions foreach ONU, among others.

Solving the upstream wavelength assignment problem economically with thearchitecture that enables the upstream transmission to use the samewavelength as that of downstream transmission for each ONU. In thisarchitecture, a wavelength router (AWG or thin film filters) is used atthe CO to route both downstream and upstream wavelengths; and there isno change to GPON/EPON power splitters based ODN

Since the upstream and downstream transmissions of each ONU share thesame wavelength, Time Division Duplex (TDD) is used for downstream andupstream traffics to avoid wavelength contingency. The downstream andupstream TDD asymmetry can be dynamically changed to fully utilize thebandwidth.

Example embodiments of a Wavelength Division Multiplex Passive OpticalNetwork (WDM PON) architecture using passive optical splitters aredisclosed herein. Disclosed WDM PON 200 as provided in FIG. 2 includesfixed wavelength optical transmitters 220 . . . 230 in Optical LineTermination (OLT) 210 system with tunable receiver colorless OpticalNetwork Units (ONUs) 260 . . . 270 that reuse the downstream light tocarry upstream data. The same wavelength may be used for downstream andupstream transmissions on single fiber 240 in ODN 215. In thisarchitecture, the number of ONUs 260 . . . 270 may be greater than thenumber of transmitters 220 . . . 230 at OLT 210 allowing for a highlyscalable system with capacity for growth. An example embodiment of thedisclosed system uses Arrayed Waveguide Grating (AWG) 235 or thin filmWDM filters at OLT 210 and passive optical splitter 255 in the field.Utilization of passive splitter based ODNs ease the migration fromcurrent Gigabit Passive Optical Network (GPON) and Ethernet PassiveOptical Network (EPON) systems to WDM PON systems.

Example embodiments of the systems and methods of wavelength divisionmultiplex passive optical networking solve the upstream wavelengthassignment problem economically with an architecture that enablesupstream transmission using the same wavelength as that of downstreamtransmission for each ONU 260 . . . 270. In an example embodiment,wavelength router (AWG or thin film filters) 235 is used at the CentralOffice to route both downstream and upstream wavelengths. There is nochange to power splitter-based ODN currently used by TDM PONs.

In an example embodiment, each of the optical signals in downstream andupstream directions is transmitted using time division duplex (TDD) on aPON. In this passive optical network, the ODN is characterized by singletrunk fiber 240 connected to power coupler 255, also called a powersplitter, that separates the downstream optical power into componentpieces. A typical example of power coupler 255 connects to 32 ONUs. Inan example embodiment, wavelength router 235 is positioned at the headend so that AWG 235 is in OLT 210. Since the transmitter is fixed, eachof the transmitter and receiver pairs 220 . . . 230 corresponds to onechannel. Transmitter/receiver pair 220 comprises a transmitter and areceiver for channel 1. Pair 230 comprises a transmitter and receiverpair for channel N. Each transmitter is configured to transmit on afixed wavelength. The transmitter of pair 220 transmits on a λ₁wavelength and is coupled to AWG 235 where it is combined with opticalsignals on the wavelengths of each of the other transmitters. Thecombined signal is transmitted along fiber 240 to passive power splitter255. Power splitter 255 passes one piece of optical signal that containsall distinguished wavelengths to each ONU 260 . . . 270 so each ONUreceives all the wavelengths transmitted on fiber 240. Each ONU 260 . .. 270 may include a filter to filter out all wavelengths but thewavelength intended for the particular ONU.

In an example embodiment, the upstream and downstream of each ONU sharethe same wavelength, transmitting in TDD mode to avoid wavelengthcontingency. The downstream and upstream transmission cycle may bedynamically changed to fully utilize the bandwidth according to theupstream and downstream traffic dynamics.

The upstream wavelengths are assigned to each ONU 260 . . . 270 byreusing the downstream light at each ONU. Previously, in downstreamlight reusing methods, the ONUs re-modulated the downstream light andsent it back to the OLT via a separate fiber. However, according to thesystems and methods disclosed herein, the transmitter at OLT 210 sendscontinuous wave (CW) downstream light and modulated downstream data toan ONU. After extracting the downstream data the ONU may use thedownstream CW light it receives to modulate upstream data and send databack to OLT 210 using the same fiber plant. In an example embodiment,one or both of the upstream and downstream transmitters uses on-offkeying (OOK), though any appropriate modulation scheme may be used.

In an example embodiment, fixed wavelengths transmitters are used at OLT210. There may be n fixed wavelength transmitters at the OLT that servem ONUs, where m is greater than or equal to n. Allowing the numbers ofONUs to exceed the transmitters in OLT 210 offers scalability to thesystem. In such an embodiment, adding an ONU does not require changingof OLT hardware. The transmitter laser is dynamically shared by multipleONUs.

FIG. 3 provides an example embodiment of WDM PON OLT design 300 withdual-band control channels as configured in the physical layers. In anexample embodiment, full-time control channel 325 may be transmitted ina dedicated wavelength such as the O band (1260 nm-1360 nm), coupled tofiber 340 at coupler 345. Additionally, part-time control channel 315may be transmitted from transmitter 320 in OLT 300 through AWG 335 andto the ONUs in the C (1530 nm-1565 nm) and/or L band (1565 nm-1625 nm).Dedicated O band control channel 325 provides reliable out-of-bandcontrol to ONUs.

FIG. 4 provides alternative embodiment 400 in which the O band controlchannel is removed in physical layers and full-time control channel 415is transmitted by transmitter 420 through AWG 435 in the C band and/or Lband onto fiber 440.

FIG. 5 provides example embodiment 500 of ONU 560 with a dedicated Oband control channel. In ONU 510, the O band control wavelength isseparated from the C band and/or L band by WDM filter 510. O bandreceiver 530 constantly receives the control signal while the OLTinstructs ONU 560 to tune to a wavelength in C band and/or L band forreceiving downstream data. After receiving the downstream data, ONU 560may use the CW light to transmit upstream data back to the OLT. Anoptical circulator 550 (between WDM 510 and tunable filter 570) may beused to separate and combine modulated downstream and upstream signals.In an example embodiment, the OLT may also send control signalsperiodically via a part-time control wavelength to all ONUs in case ofproblems with the O band control channel. In an example embodiment, ONU560 tunes to the wavelength λ₀ of the O band control channel by defaulton initial boot up.

OLT also sends CW light periodically via O band control wavelength λ₀ toall ONUs. In case that an ONU does not receive downstream data but hasupstream data to send, it may send the wavelength setup request byremodulating the CW light received from the O band control channel.Since most of the control command from the OLT are sent to ONUs throughan O band control channel, the C band and/or L band part-time controlchannel may be used to carry user data as well. The downstream andupstream transmission asymmetry may be dynamically negotiated betweenthe OLT and ONU 560. Once ONU 560 has been assigned a wavelength,in-band control may also be established as the part of the protocol.

WDM filter 510 separates the O band control channel from the rest of theC band and/or L band channels. O band receiver 530 decodes the controlsignal. One part of the decoded control signal is used to controltunable filter 570 for selecting the wavelength assigned to ONU 560 bythe OLT. The rest of the decoded control signal is sent to MAC layer 590to control the upstream transmission cycle. The downstream lightcontaining multiple wavelength channels from WDM filter 510 is sent tooptical circulator 550 and is passed to tunable filter 570 which selectsthe assigned wavelength.

The selected wavelength channel that contains CW light and modulateddata signal is separated into two pieces by 1×2 splitter 580. A firstpiece with the modulated data signal is sent to optical receiver 585 fordecoding downstream user date. The CW light is filtered out. The decodeduser data is sent to MAC and higher layers 590 for further processing.The second piece with CW light is sent to modulator 520 for modulatingupstream data. The original modulated downstream data is filtered out atthe upstream receiver at OLT. The modulated optical signal is sentupstream via optical circulator 550.

In example embodiment 600 of ONU 660 of FIG. 6, a C band and/or L bandwavelength λ_(i) may be used as a full-time control channel. When ONU660 initially performs a boot up sequence, ONU 660 tunes to wavelengthλi by default. Using this control channel, the OLT instructs ONU 660 totune to a wavelength in C band and/or L band for receiving downstreamdata. After receiving the downstream data, ONU 660 can use the CW lightto transmit upstream data back to OLT. Optical circulator 650 (beforetunable filter 670) is used to separate and combine modulated downstreamand upstream lights. Once ONU 660 has been assigned a wavelength,in-band control may also be established as the part of the protocol.

The incoming downstream light is passed by optical circulator 650 totunable optical filter 670. The predefined control wavelength channelλ_(i) is decoded. The decoded control signal is used to control tunablefilter 670 for selecting the wavelength assigned to ONU 660 by the OLT.The selected wavelength channel that contains CW light and modulateddata signal is separated into two pieces by 1×2 splitter 680. The firstpiece with the modulated data signal is sent to optical receiver 630 fordecoding downstream user data. The CW light is filtered out. The decodeduser data is sent to MAC and higher layers 690 for further processing.The second piece with CW light is sent to modulator 620 for modulatingupstream data. The original modulated downstream data is filtered out atthe upstream receiver at the OLT. The modulated optical signal is sentupstream from modulator 620 via optical circulator 650.

The OLT also sends CW light periodically via control wavelength λi toall ONUs connected to the power splitter. In a case in which ONU 660does not receive downstream data but has upstream data to send, ONU 660may send a wavelength setup request by re-modulating the CW lightreceived from the C band and/or L band control channel. The TDDasymmetry of downstream and upstream transmissions may be dynamicallynegotiated between the OLT and ONU 660.

An example embodiment of WDM PON architecture with dual-band controlswith the ONU of FIG. 5 is provided in FIG. 7. OLT 705 uses fixedwavelength dense wavelength division multiplexing (DWDM) gradedistributed feedback (DFB) laser transmitters as an example lightsource. The flexibility of the architecture is realized by employingtunable optical filters at ONUs 760 . . . 770. Power splitter based WDMPON may employ optical filter 755 at ONUs 760 . . . 770 in an exampleembodiment.

WDM PON 700 includes fixed wavelength optical transmitters 720 . . . 730in Optical Line Termination (OLT) 705 with tunable receiver colorlessOptical Network Units (ONUs) 760 . . . 770 that reuse the downstreamlight to carry upstream data. The same wavelength may be used fordownstream and upstream transmissions on single fiber 740. In thisarchitecture, the number of ONUs 760 . . . 770 may be greater than thenumber of transmitters 720 . . . 730 at OLT 705. An example embodimentof the disclosed system uses Arrayed Waveguide Grating (AWG) 735 or WDMfilters at OLT 705 and passive optical splitter 755 in the field. In anexample embodiment, wavelength router (AWG or thin film filters) 735 isused at the Central Office to route both downstream and upstreamwavelengths. There is no change to power splitter-based ODN thatcurrently use GPON/EPON.

In an example embodiment, wavelength router 735 is positioned at thehead-end so that AWG (as an example) 735 is in OLT 705. Since thetransmitter is fixed, each of the transmitter and receiver pairs 720 . .. 730 corresponds to one channel. Transmitter/receiver pair 720comprises a transmitter and a receiver for channel 1. Pair 730 comprisesa transmitter and receiver pair for channel N. Each transmitter isconfigured to transmit on a fixed wavelength. The transmitter of pair720 transmits on a λ₁ wavelength and is coupled to AWG 735 where it iscombined with signals on the wavelengths of each of the othertransmitters. The combined signal is transmitted along fiber 740 topower splitter 755. Power splitter 755 passes the several distinguishedwavelengths to each ONU 760 . . . 770 so each ONU receives all thewavelengths transmitted on fiber 740. Each ONU 760 . . . 770 may includea filter to filter out all wavelengths but the wavelength intended forthe particular ONU.

In an example embodiment, the upstream and downstream of each ONU sharethe same wavelength, transmitting in TDD mode to avoid wavelengthcontingency. The downstream and upstream transmission cycle may bedynamically changed to fully utilize the bandwidth according to theupstream and downstream traffic dynamics.

In an example embodiment, fixed wavelengths transmitters are used at OLT705. There may be n fixed wavelength transmitters at OLT 705 that servem ONUs, where m is greater than or equal to n. Allowing the numbers ofONUs to exceed the transmitters in OLT 705 offers scalability to thesystem. In such an embodiment, adding an ONU does not require changingof OLT hardware.

Example embodiments of ONUs 760, 770 employ a dedicated O band controlchannel. In ONU 760, 770, the O band control wavelength is separatedfrom the C band and/or L band by WDM filter 757, 777. O band receiver766, 776 constantly receives the control signal while OLT 705 instructsONU 760, 770 to tune to a wavelength in C band and/or L band forreceiving downstream data. After receiving the downstream data, ONU 760,770 may use the CW light to transmit upstream data back to OLT 705. Anoptical circulator (between WDM 757, 777 and tunable filter 764, 774)may be used to separate and combine modulated downstream and upstreamsignals. In an example embodiment, OLT 705 may also send control signalsperiodically via a part-time control wavelength to all ONUs in case ofproblems with the O band control channel. In an example embodiment, ONU760, 770 tunes to wavelength λ₀ of the O band control channel by defaulton initial boot up.

WDM filter 757, 777 separates the O band control channel from the restof the C band and/or L band channels. O band receiver 766, 776 decodesthe control signal. One part of the decoded control signal is used tocontrol tunable filter 764, 774 for selecting the wavelength assigned toONU 760 . . . 770 by the OLT. The rest of the decoded control signal issent to MAC layer 762, 772 to control the upstream transmission cycle.The downstream light containing multiple wavelength channels from WDMfilter 757, 777 is sent to the optical circulator and is passed totunable filter 764, 774 which selects the assigned wavelength.

The selected wavelength channel that contains CW light and modulateddata signal is separated into two pieces by 1×2 splitter 768, 778. Afirst piece with the modulated data signal is sent to an opticalreceiver for decoding downstream user date. The CW light is filteredout. The decoded user data is sent to MAC and higher layers 762, 772 forfurther processing. The second piece with CW light is sent to modulator759, 779 for modulating upstream data. The original modulated downstreamdata is filtered out at the upstream receiver at OLT. The modulatedoptical signal is sent to the upstream via the optical circulator.

OLT 705 also sends CW light periodically via O band control wavelengthλ₀ to all ONUs. In case that an ONU does not receive downstream data buthas upstream data to send, it may send the wavelength setup request byremodulating the CW light received from the O band control channel.Since most of the control command from OLT 705 are sent to ONUs throughan O band control channel, the C band and/or L band part-time controlchannel may be used to carry user data as well. The downstream andupstream transmission asymmetry may be dynamically negotiated betweenOLT 705 and ONU 760, 770. Once ONU 760, 770 has been assigned awavelength, in-band control may also be established as the part of theprotocol.

FIG. 8 provides an example embodiment of WDM architecture with signalcontrol channel provided in FIG. 6. In this example embodiment, the Oband control channel has been removed to simplify the design. Therefore,the C band and/or L band control channel becomes full-time, i.e., itwill be dedicated for control only. OLT 805 uses fixed wavelength densewavelength division multiplexing (DWDM) grade distributed feedback (DFB)laser transmitters as an example light source. The flexibility of thearchitecture is realized by employing tunable optical filters at ONUs860 . . . 870. Power splitter based WDM PON may employ optical filter864, 874 at ONUs 860 . . . 870 in an example embodiment.

WDM PON 800 includes fixed wavelength optical transmitters 820 . . . 830in Optical Line Termination (OLT) 805 with tunable receiver colorlessOptical Network Units (ONUs) 860 . . . 870 that reuse the downstreamlight to carry upstream data. The same wavelength may be used fordownstream and upstream transmissions on single fiber 840. In thisarchitecture, the number of ONUs 860 . . . 870 may be greater than thenumber of transmitters 820 . . . 830 at OLT 805. An example embodimentof the disclosed system uses Arrayed Waveguide Grating (AWG) 835 or WDMfilters at OLT 805 and passive optical splitter 855 in the field. In anexample embodiment, wavelength router (AWG or thin film filters) 835 isused at the Central Office to route both downstream and upstreamwavelengths. There is no change to GPON/EPON power splitter-based ODN.

In an example embodiment, wavelength router 835 is positioned at thehead end so that AWG (as an example) 835 is in OLT 805. Since thetransmitter is fixed, each of the transmitter and receiver pairs 820 . .. 830 corresponds to one channel. Transmitter/receiver pair 820comprises a transmitter and a receiver for channel 1. Pair 830 comprisesa transmitter and receiver pair for channel N. Each transmitter isconfigured to transmit on a fixed wavelength. The transmitter of pair820 transmits on a λ₁ wavelength and is coupled to AWG 835 where it iscombined with signals on the wavelengths of each of the othertransmitters. The combined signal is transmitted along fiber 840 topower splitter 855. Power splitter 855 passes the several distinguishedwavelengths to each ONU 860 . . . 870 so each ONU receives all thewavelengths transmitted on fiber 840. Each ONU 860 . . . 870 may includea filter to filter out all wavelengths but the wavelength intended forthe particular ONU.

In an example embodiment, the upstream and downstream of each ONU sharethe same wavelength, transmitting in TDD mode to avoid wavelengthcontingency. The downstream and upstream transmission cycle may bedynamically changed to fully utilize the bandwidth according to theupstream and downstream traffic dynamics.

In an example embodiment, fixed wavelengths transmitters are used at OLT805. There may be n fixed wavelength transmitters at OLT 805 that servem ONUs, where m is greater than or equal to n. Allowing the numbers ofONUs to exceed the transmitters in OLT 805 offers scalability to thesystem. In such an embodiment, adding an ONU does not require changingof OLT hardware.

In example embodiment of ONU 860, 870, a C band and/or L band wavelengthλ_(i) may be used as a full-time control channel. When ONU 860, 870initially performs a boot up sequence, ONU 860, 870 tunes to wavelengthAi by default. Using this control channel, OLT 805 instructs ONU 860,870 to tune to a wavelength in C band and/or L band for receivingdownstream data. After receiving the downstream data, ONU 860, 870 mayuse the CW light to transmit upstream data back to OLT 805. An opticalcirculator (before tunable filter 864, 874) is used to separate andcombine modulated downstream and upstream lights. Once ONU 860, 870 hasbeen assigned a wavelength, in-band control may also be established asthe part of the protocol.

The incoming downstream light is passed by an optical circulator totunable optical filter 864, 874. The predefined control wavelengthchannel λ_(i) is decoded. The decoded control signal is used to controltunable filter 864, 874 for selecting the wavelength assigned to ONU 860. . . 870 by the OLT. The selected wavelength channel that contains CWlight and modulated data signal is separated into two pieces by 1×2splitter 868, 878. The first piece with the modulated data signal issent to optical receiver 866, 876 for decoding downstream user data. TheCW light is filtered out. The decoded user data is sent to MAC andhigher layers 862, 872 for further processing. The second piece with CWlight is sent to modulator 859, 879 for modulating upstream data. Theoriginal modulated downstream data is filtered out at the upstreamreceiver at the OLT. The modulated optical signal is sent upstream frommodulator 859, 879 via the optical circulator.

OLT 805 also sends CW light periodically via control wavelength λi toall ONUs connected to the power splitter. In a case in which ONU 860,870 does not receive downstream data but has upstream data to send, ONU860, 870 may send a wavelength setup request by re-modulating the CWlight received from the C band and/or L band control channel. The duplexasymmetry of downstream and upstream transmissions may be dynamicallynegotiated between the OLT and the ONU.

In an example embodiment, high power lasers may be used at the OLT toeliminate the use of optical amplifiers at the ONUs. However, an SOA(Semiconductor Optical Amplifier) may be used at the ONU to boot up theoptical signal before it is fed into the modulator. FIG. 9. provides theONU design of FIG. 7 with SOA 961 between splitter 968 and modulator959. In example embodiment 900 of ONU 960, a C band and/or L bandwavelength λ_(i) may be used as a full-time control channel. When ONU960 initially performs a boot up sequence, ONU 960 tunes to wavelengthλi by default. Using this control channel, the OLT instructs ONU 960 totune to a wavelength in C band and/or L band for receiving downstreamdata. After receiving the downstream data, ONU 960 can use the CW lightto transmit upstream data back to OLT. An optical circulator (beforetunable filter 964) is used to separate and combine modulated downstreamand upstream lights. Once ONU 960 has been assigned a wavelength,in-band control may also be established as the part of the protocol.

The incoming downstream light is passed by an optical circulator totunable optical filter 964. The predefined control wavelength channelλ_(i) is decoded. The decoded control signal is used to control tunablefilter 964 for selecting the wavelength assigned to ONU 960 by the OLT.The selected wavelength channel that contains CW light and modulateddata signal is separated into two pieces by 1×2 splitter 980. The firstpiece with the modulated data signal is sent to optical receiver 966 fordecoding downstream user data. The CW light is filtered out. The decodeduser data is sent to MAC and higher layers 962 for further processing.The second piece with CW light is sent to through SOA 961 foramplification to modulator 959 for modulating upstream data. Theoriginal modulated downstream data is filtered out at the upstreamreceiver at the OLT. The modulated optical signal is sent upstream frommodulator 959 via the optical circulator.

The OLT also sends CW light periodically via control wavelength λi toall ONUs connected to the power splitter. In a case in which ONU 960does not receive downstream data but has upstream data to send, ONU 960may send a wavelength setup request by re-modulating the CW lightreceived from the C band and/or L band control channel. The duplexasymmetry of downstream and upstream transmissions may be dynamicallynegotiated between the OLT and ONU 960.

FIG. 10 provides the ONU design of FIG. 6 with SOA 1061 between splitter1068 and modulator 1059. FIG. 10 provides example embodiment 1000 of ONU1060 with a dedicated O band control channel. In ONU 1060, the O bandcontrol wavelength is separated from the C band and/or L band by WDMfilter 1057. O band receiver 1066 constantly receives the control signalwhile the OLT instructs ONU 1060 to tune to a wavelength in C bandand/or L band for receiving downstream data. After receiving thedownstream data, ONU 1060 may use the CW light to transmit upstream databack to the OLT. An optical circulator (between WDM 1057 and tunablefilter 1064) may be used to separate and combine modulated downstreamand upstream signals. WDM filter 1057 separates the O band controlchannel from the rest of the C band and/or L band channels. In anexample embodiment, the OLT may also send control signals periodicallyvia a part-time control wavelength to all ONUs in case of problems withthe O band control channel. In an example embodiment, ONU 1060 tunes tothe wavelength λ₀ of the O band control channel by default on initialboot up.

WDM filter 1057 separates the O band control channel from the rest ofthe C band and/or L band channels. O band receiver 1066 decodes thecontrol signal. One part of the decoded control signal is used tocontrol tunable filter 1064 for selecting the wavelength assigned to ONU1060 by the OLT. The rest of the decoded control signal is sent to MAClayer 1062 to control the upstream transmission cycle. The downstreamlight containing multiple wavelength channels from WDM filter 1057 issent to the optical circulator and is passed to tunable filter 1064which selects the assigned wavelength.

The selected wavelength channel that contains CW light and modulatedoptical signal is separated into two pieces by 1×2 splitter 1068. Afirst piece with the modulated data signal is sent to optical receiver1066 for decoding downstream user date. The CW light is filtered out.The decoded user data is sent to MAC and higher layers 1062 for furtherprocessing. The second piece with CW light is sent through SOA 1061 foramplification and to modulator 1059 for modulating upstream data. Theoriginal modulated downstream data is filtered out at the upstreamreceiver at OLT. The modulated optical signal is sent to the upstreamvia the optical circulator.

The OLT also sends CW light periodically via O band control wavelengthλ₀ to all ONUs. In case that an ONU does not receive downstream data buthas upstream data to send, it may send the wavelength setup request byremodulating the CW light received from the O band control channel.Since most of the control command from the OLT are sent to ONUs throughan O band control channel, the C band and/or L band part-time controlchannel may be used to carry user data as well. The downstream andupstream transmission asymmetry may be dynamically negotiated betweenthe OLT and ONU 1060. Once ONU 1060 has been assigned a wavelength,in-band control may also be established as the part of the protocol.

FIG. 11 provides flow chart 1100 of an example embodiment of a method ofwavelength division multiplex passive optical networking. In block 1110,a data signal is received. In block 1120, the data signal is modulatedwith an optical line termination transmission laser at a particularwavelength. In block 1130, the modulated signal is transmitted to aduplex filter for transmission on a single fiber optical distributionnetwork.

The flow chart of FIG. 11 shows the architecture, functionality, andoperation of a possible implementation of the wavelength divisionmultiplex passive optical networking software. In this regard, eachblock represents a module, segment, or portion of code, which comprisesone or more executable instructions for implementing the specifiedlogical function(s). It should also be noted that in some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in FIG. 11. For example, two blocks shown in succession inFIG. 11 may in fact be executed substantially concurrently or the blocksmay sometimes be executed in the reverse order, depending upon thefunctionality involved. Any process descriptions or blocks in flowcharts should be understood as representing modules, segments, orportions of code which include one or more executable instructions forimplementing specific logical functions or steps in the process, andalternate implementations are included within the scope of the exampleembodiments in which functions may be executed out of order from thatshown or discussed, including substantially concurrently or in reverseorder, depending on the functionality involved. In addition, the processdescriptions or blocks in flow charts should be understood asrepresenting decisions made by a hardware structure such as a statemachine.

The logic of the example embodiment(s) can be implemented in hardware,software, firmware, or a combination thereof. In example embodiments,the logic is implemented in software or firmware that is stored in amemory and that is executed by a suitable instruction execution system.If implemented in hardware, as in an alternative embodiment, the logiccan be implemented with any or a combination of the followingtechnologies, which are all well known in the art: a discrete logiccircuit(s) having logic gates for implementing logic functions upon datasignals, an application specific integrated circuit (ASIC) havingappropriate combinational logic gates, a programmable gate array(s)(PGA), a field programmable gate array (FPGA), etc. In addition, thescope of the present disclosure includes embodying the functionality ofthe example embodiments disclosed herein in logic embodied in hardwareor software-configured mediums.

Software embodiments, which comprise an ordered listing of executableinstructions for implementing logical functions, can be embodied in anycomputer-readable medium for use by or in connection with an instructionexecution system, apparatus, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions. In the context of this document, a“computer-readable medium” can be any means that can contain, store, orcommunicate the program for use by or in connection with the instructionexecution system, apparatus, or device. The computer readable medium canbe, for example but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, ordevice. More specific examples (a nonexhaustive list) of thecomputer-readable medium would include the following: a portablecomputer diskette (magnetic), a random access memory (RAM) (electronic),a read-only memory (ROM) (electronic), an erasable programmableread-only memory (EPROM or Flash memory) (electronic), and a portablecompact disc read-only memory (CDROM) (optical). In addition, the scopeof the present disclosure includes embodying the functionality of theexample embodiments of the present disclosure in logic embodied inhardware or software-configured mediums.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade thereto without departing from the spirit and scope of theinvention as defined by the appended claims.

Therefore, at least the following is claimed:
 1. A system comprising: anoptical line termination (OLT) transmitter laser of a plurality of OLTtransmitter lasers configured to transmit at a particular wavelength;and a wavelength router configured to couple a downstream optical signalfrom the OLT transmitter laser onto a single fiber optical distributionnetwork for reception by a passive optical power splitter, thewavelength router further configured to receive an upstream opticalsignal from the single fiber optical distribution network and route theupstream data signal to an appropriate receiver, the OLT configured totransmit a part-time control channel in the C band (1530 nm-1565 nm)and/or the L band (156 nm-1625 nm).
 2. The system of claim 1, whereinthe wavelength router is at least one of an arrayed waveguide grating(AWG) and a thin film filter.
 3. The system of claim 1, wherein the OLTtransmitter laser transmits continuous wave light with an on-off keyingmodulated optical signal.
 4. The system of claim 1, wherein the OLTtransmitter laser is further configured to transmit a control channel onthe O band (1260 nm-1360 nm).
 5. The system of claim 4, wherein the Oband control channel is coupled to an output of the wavelength routerwith a wavelength division multiplexing multiplier.
 6. The system ofclaim 1, further comprising a plurality of optical network unitstransmitting both upstream and downstream on the same wavelength in timedivision duplex mode.
 7. The system of claim 1, wherein the OLTtransmitter laser is further configured to transmit a full-time controlchannel in the C band (1530 nm-1565 nm) and/or the L band (156 nm-1625nm).
 8. The system of claim 1, wherein the OLT transmitter laser iscoupled to the wavelength router with an optical circulator.
 9. Thesystem of claim 1, further comprising an optical network unit configuredto receive an optical signal on the particular wavelength from a passiveoptical power splitter and send an upstream optical signal on the samewavelength.
 10. The system of claim 9, wherein the upstream signal anddownstream signal are transmitted in time division duplex mode.
 11. Amethod comprising receiving a data signal; modulating the data signalwith an optical line termination transmitter laser at a particularwavelength; transmitting the modulated signal to a wavelength router fortransmission on a single fiber optical distribution network; andtransmitting a part-time control channel in the C band (1530 nm-1565 nm)and/or the L band (156 nm-1625 nm).
 12. The method of claim 11, furthercomprising modulating the light using on-off keying.
 13. The method ofclaim 11, further comprising transmitting the light in a continuouswave.
 14. The method of claim 11, further comprising transmitting acontrol channel on the O band (1260 nm-1360 nm).
 15. The method of claim14, further comprising coupling the O band control channel to an outputof the wavelength router with a wavelength division multiplexingmultiplier.
 16. The method of claim 14, further comprising transmittingboth upstream and downstream on the same wavelength in time divisionduplex mode.
 17. The method of claim 11, further comprising transmittinga full-time control channel in the C band (1530 nm-1565 nm) and/or the Lband (156 nm-1625 nm).
 18. A system comprising. an optical linetermination (OLT) transmitter laser of a plurality of OLT transmitterlasers configured to transmit at a particular wavelength and to transmita part-time control channel in the C band (1530 nm-1565 nm) and/or the Lband (156 nm-1625 nm); a wavelength router configured to couple adownstream optical signal from the OLT transmitter laser onto a singlefiber optical distribution network for reception by a passive opticalpower splitter, the wavelength router further configured to receive anupstream optical signal from the single fiber optical distributionnetwork and route the upstream optical signal to an appropriatereceiver; a plurality of optical network units (ONUs) configured toreceive downstream optical signals and transmit upstream opticalsignals; and a passive optical power splitter configured to route thedownstream optical signal to a particular ONU of the plurality of ONUsbased on the received wavelength.
 19. The system of claim 18, whereinthe particular ONU is configured to send an upstream optical signal onthe same wavelength on which it received the downstream optical signal.20. The system of claim 19, wherein the upstream optical signal anddownstream optical signal are transmitted in half duplex mode.